1. Field of the Invention
This invention relates to a sustained release drug delivery device and, in particular, to a device for the transdermal or percutaneous delivery of drugs. The invention relates especially to a device for the systemic delivery of drugs by the transdermal route.
2. Description of the Prior Art
The advantages of administering certain drugs by the transdermal route are well known and include avoidance of drug deactivation by digestive enzymes or first-pass hepatic metabolism. However, these advantages are also characteristic of drug administration by parenteral routes such as by intramuscular injection or i.v. infusions.
Until relatively recently--circa 1980--only parenteral administration offered precise control over rate of drug entry into the bloodstream and then only when closely monitored.
A number of transdermal devices have now been developed and consist essentially of transdermal or skin patches. Certain of these transdermal devices include a rate-controlling membrane between a drug reservoir and the skin surface. The rate-controlling membrane limits the amount of drug delivered per unit area of skin surface in a manner such that the device and not the skin is dominant in controlling the rate of drug input to the skin surface and hence to the systemic circulation.
One of the first rate-controlled transdermal products was a transdermal form of scopolamine indicated for the prevention of nausea and vomiting induced by motion and known as the transdermal therapeutic system--scopolamine (TTS-scopolamine). This product, which is manufactured by Alza Corporation, California, U.S.A., is described in a paper by Shaw, J. and Urquhart J. entitled "Programmed, systemic drug delivery by the transdermal route" TIPS--April 1980, at page 208. TTS-scopolamine is also the subject of a paper by Price et al. in Clinical Therapeutics Vol. 2 No. 4, 1979.
The TTS-scopolamine system functions by permitting the drug which is highly concentrated in a small reservoir, to diffuse through a dense or microporous rate-controlling membrane. The driving force of this system, the concentration gradient of drug across the membrane, is established by the difference between the concentration of drug in the reservoir and that outside the membrane. The rate of drug release is determined by the properties of the membrane and the difference in drug concentration across the membrane.
A number of transdermal nitroglycerin patches are now on the U.S. market and are indicated for the prevention and treatment of angina pectoris due to coronary artery diseases. Although there are differences in composition, mechanism of drug delivery and appearance among the currently available transdermal nitroglycerin devices all appear to be functionally similar.
Only Ciba Pharmaceutical Company markets a transdermal nitroglycerin-patch with a rate-controlling outer membrane. An equivalent product manufactured by Key Pharmaceuticals, Inc. and sold under the trademark NITRO-DUR includes a diffusion matrix wherein nitroglycerin molecules are in equilibrium between lactose crystals and a liquid phase. When the matrix is applied to the skin, nitroglycerin molecules migrate by diffusion to the skin providing a constant flow of drug into the systemic circulation (c.f. American Pharmacy Vol. NS22 No. 2, February 1982/85).
All the currently available transdermal devices are secured to the skin by a layer of adhesive. In the case of the abovementioned transdermal nitroglycerin patches it is recommended that the patches be applied to a hairless region of the body such as the upper arm or chest. Shaving of a suitable area for application of the patch may be necessary. However, shaving may cause local skin irritation and change the permeability characteristics of the products. All the currently available transdermal products are approved for once-daily administration and it is recommended that one alternates application sites daily.
It will be appreciated that the repeated application and removal of such patches, involving a securing layer of adhesive, can result in skin irritation and sensitization with prolonged use. It will also be appreciated that a certain amount of pain and discomfort is experienced on removing the patches.
Literature supplied with the currently available transdermal devices indicates that patients may bathe or shower while wearing the products. However, a transdermal device which could be readily removed when bathing or showering would be considerably more desirable.
It is an object of the present invention to provide a transdermal device which overcomes the aforementioned disadvantages of known transdermal devices and which is convenient to use, readily removable while performing functions such as bathing or showering, cosmetically acceptable and provides the user with a degree of privacy.